Iagpo, Igarape, Varzea...and the abundance within them

If you've followed Tannin Aquatics for any length of time, you know all to well that we're pretty much obsessed with some of the ephemeral aquatic habitats of South America, ranging from flooded forests to seasonally inundated grasslands, and even temporary streams which flow through the forest.

We're drawn to these habitats because they are inspiring examples of how the terrestrial and aquatic environments work together. 

In these wild habitats, the leaves, branches, soils, and other botanical materials which are present during the dry season, remain in place, or are added to by dynamic, seasonal processes. For the most part, the soil, branches, and a fair amount of the more "durable" seed pods and such remain present during both phases.

The formerly terrestrial physical environment is now transformed into an earthy, twisted, incredibly rich aquatic habitat, which fishes have evolved over eons to live in and utilize for food, protection, and complex, protected spawning areas. 

All of the botanical material-shrubs, grasses, fallen leaves, branches, seed pods, and such, is suddenly submerged; often, currents re-distribute the leaves and seed pods and branches into little pockets and "stands", affecting the (now underwater) "topography" of the landscape.

Leaves begin to accumulate. Detritus settles on the substrate, leaves, and fallen branches.

Soils dissolve their chemical constituents- tannins, filmic, and humic acids- into the water, enriching it. Fungi and micororganisms begin to colonize on the fallen tree trunks, seed pods, and leaves, breaking down the materials. Biofilms form, crustaceans and aquatic insects multiply rapidly. Fishes are able to find new food sources; new hiding places..new areas to spawn.

Life simply flourishes.

And it is part of a sequence. A pattern...A journey. Perhaps what could best be called an evolution- which Nature has carefully set up and managed over eons. 

These habitats are "seasonally inundated" by the significant rainfall common ottos region; some of these forests may be submerged for almost half a year...that's a LOT of water! Like, 3%-4% of the water in the Amazon Basin at any given time...And these are precious, diverse natural treasures, so replicating one in the home aquarium is another way to learn and teach more about them, isn't it?


Igapo forests have a pretty significant amount of trees; one study found that over 30 species of trees are found in these areas, creating coverage of something on the order of 30%, and are known to have soils that are acidic in nature, yet low in nutrient content (because they don't receive a seasonal influx of nutrients like regions called "varzea", which are flooded by sediment-laden "whitewater" rivers).

The water depth in these habitats can vary from as little as 6-8 inches ( 15.24cm- 20.32cm), to almost 20 feet (6.96m)!  And of course, they have a lot of tannins, filmic, and humic substances in them from all of the soil and plant materials.

Igapo remain surprisingly "nutrient poor" by ecological standards, because the nutrient-rich alluvial sediments from the Andes, carried by whitewater rivers, which are deposited into the varzea forests annually, don't find their way into these habitats. 

Another interesting thing about Amazonian streams and flooded forest areas in general is that there is no significant "in situ" (in place) primary production, and that the fish populations that reside in them depend on what is known as "allochthonous input" (material that is imported into an ecosystem from outside of it) from materials like seed pods, fruits, blossoms, leaves, and dead wood from the surrounding forest.

This is why leaf litter beds are so important in blackwater habitats, as they serve as sort of "aggregators" of terrestrial material, and foster decay and biological processes which support what aquatic ecologists call  "food webs." Most of the aquatic life forms which reside in these waters are aggregated in submerged litter.

These inundated forest floors are fascinating subjects for aquarium replication! You get all sorts of interesting interactions, interdependencies, and relationships in one convenient package, lol.

As we mentioned before, the soils in these forests are typically acidic and sandy. The tributaries that flood them are often covered with a whitish, fine-grained sand, and lots of sediment, which is commonly found in this habitat after the inundation. So, from an aesthetic and functional standpoint, many of the aquarium-specific sands that we play with in the hobby are perfect for this type of simulation.

In a comparative study of Amazonian fish diversity and density conducted by Henderson and Crampton in 1994, in nutrient poor blackwater igapó at the blackwater sites had moderate turbidity, a very low conductivity, and a pH of 5.3-6.0. A more recent study I stumbled upon indicated a pH range of 3.4-5.5, so it really depends on the specific locale, the length of time that the forest has been inundated, and the density and quantity of the leaves and other plant materials which accumulate on the substrate. 

Replicating the dynamics and some of the characteristics in these habitats is something that we've been experimenting with for several years, with impressive and intriguing results.

We've tackled our "Urban Igapo" idea a bunch of times here in "The Tint", with the technique being described and studied quite a bit. Now, the repetition of wet and dry "seasonal cycles" in the aquarium, although fascinating and the most novel takeaway from this approach, is but one way to apply the idea of evolving a "dry forest floor" into an aquatic habitat.

This is one of the most incredible and fascinating ecological dynamics in Nature, and it's something that we as a hobby have not attempted to model to any extent, until we started messing around with the idea of replicating it around 2017. Again, we're not talking about replicating the 'look" of a flooded forest after it's been flooded...That has been done for years by hobbyists, particularly in biotope design contests. An "aquascaping" thing. 

This is a bit different. 

We're talking about actually replicating and flooding the forest floor! Replicating the cycle of inundation. It's a functional approach, requiring understanding, research, and patience to execute. And the aesthetics? They will follow, resembling what you see in Nature. And that's certainly "different" than what many might expect. But the primary reason we've been playing with replicating these habitats is NOT for aesthetics... 


The approach and process is straightforward: You utilize a sedimented substrate (um, yeah, we do make one 😆) to create a "forest floor." And then, you add leaves, botanicals, and perhaps, some terrestrial grass seeds, and even riparian plants.

You'd set whatever "hardscape" you want- driftwood, etc. in place. Of course, you'd have to water your little forest floor for some period of time, allowing the vegetation to sprout and grow. Based on the many times of played with the "Igapo" idea, this process typically takes around 2-3 months to establish the growth well. 

And then what? Well, you'd flood it!

You could do this all at one time, or over the course of several  days or weeks, depending upon your preference. I mean, shit- you've waited a couple of months just to add water to your tank...what's another few days? 😆 Now, sure, there's a difference between a 5-gallon tank and a 50- gallon tank, and it takes a lot longer to fill, so it's up to you how you want to approach this!

So, yeah, the execution of this type of aquarium is not all that difficult.

And what you'll initially end up with is a murky, tinted environment, with little bits of leaves, botanicals, and soil floating about. Sounds like a blast, huh? And when you think about it, this is not all that different, at least procedurally, from the "dry start" approach to a planted tank...except we're not talking about a planted tsmnk here.. I mean, you could do aquatic plants...but it's more of a "wholistic biome" approach...

The interesting thing about this approach is that you will see a tank which "cycles" extremely quickly, in my experience. In fact, Iv'e done many iterations of "Urban Igapo" tanks where there was no detectible "cycle" in the traditional sense. I don't have an explanation for this, except to postulate that the abundance of bacterial and microorganism growth, and other life forms, like fungal growths, etc., powered by the nutrients available to them in the established terrestrial substrate simply expedites this process dramatically.


That's my theory, of course, and I could be way, way off base, but it is based on my experience and that of others in our community over the past several years. I mean, there is a nitrogen cycle occurring in the dry substrate, so when it's inundated, do the bacteria make the transition, or do they perish, followed by the very rapid colonization by other species, or..?


An underwater biome is created immediately with this approach. Doing this type of "transition" is going to not only create a different sort of underwater biodiversity, it will have the "collateral benefit" of creating a very different aesthetic as well. And yeah, it's an aesthetic that will be dictated by Nature, and will encompass all of those things that we know and love- biofilms, fungal growth, decomposition, etc.

From an aquarium perspective, the unique ecology of these types of habitats lend themselves very well to aquarium replication. Because they encourage an explosion of life forms- a "bloom", if you will- at all levels, something which we should all celebrate. 

Nature celebrates "The Bloom", too.

And yeah, there is something truly remarkable about natural processes playing out in our own aquariums, as they have done for eons in the wild.

Remember, it's all part of the game with a botanical-influenced aquarium. Understanding, accepting, and celebrating  that "the bloom" is all part of that "mental shift" towards accepting and appreciating a more truly natural-looking, natural-functioning aquarium. The "price of admission", if you will- along with the tinted water, decomposing leaves, etc., the metaphorical "dues" you pay, which ultimately go hand-in-hand with the envious "ohhs and ahhs" of other hobbyists who admire your completed aquarium when they see it for the first time.


The reality to us as "armchair ecologists" is that the presence of these organisms in our aquariums is beautiful to us for so many reasons. It's not only a sign that our closed microcosms are functioning well, but that they are, in their own way, providing for the well- being of the inhabitants! 

An abundance, created by the explosion of life in our tanks, filed by botanical materials.

The "mental stretches" that we ask you to make to accept these organisms and their appearance really require us to look at the wild habitats from which our fishes come, and reconcile that with our century-old aquarium hobby idealization of what Nature (and therefore our "natural" aquariums) actually look like.

Sure, it's not an easy stretch for most. Seeing it in Nature and seeing it in your home aquarium are two very different things...

It's likely not everyone's idea of "attractive", and you'd no doubt freak out snobby contest judges with a tank full of biofilms and fungi, but to most of us, we should take great delight in knowing that we are providing our fishes with an extremely natural component of their ecosystem, the benefits of which have never really been studied in the aquarium in depth.

Why? Well, because we've been too busy looking for ways to remove the stuff instead of watching our fishes feed on it, and our aquatic environments benefit from its appearance!

We've had it all wrong, IMHO. 

It's okay, we're starting to come around...

Welcome to Planet Earth.

Yet, there are always those doubts...and some are not willing to sit by and watch the "slime" take over...despite the fact that we know it's okay...

Celebrate "The Bloom." Savor the abundance.

Blurring the lines between Nature and the aquarium, from an aesthetic sense, at the very least- and in many respects, from a "functional" sense as well, proves just how far hobbyists have come...how good you are at what you do. And... how much more you can do when you turn to nature as an inspiration, and embrace it for what it is.

The same processes which occur on a grander scale in Nature also occur on a "micro-scale" in our aquariums. And we can understand and embrace these processes- rather than resist or even "revile" them- as an essential part of the aquatic environment.

And the beauty of it all is that your aquarium will evolve over time, as the botanical materials break down and impart their chemical constituents into the water. The water clears, taking on a deep tint..all of the aesthetics that we seem to crave when we get into this type of aquarium in the first place.

It just takes a little time...and a lot of patience on your part.

So it really doesn't matter which habitat you're attempting to replicate in your aquarium- it's more of a matter of how you do it. And how you react when you do it.

Either way, as the sayings goes...just DO it.

Stay creative. Stay inspired. Stay observant. Stay patient. Stay bold...

And Stay Wet.


Scott Fellman

Tannin Aquatics


Scott Fellman
Scott Fellman


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